The present invention relates to a method of manufacturing complex esters of high purity from olefin, carbon monoxide, polyalcohol and polycarboxylic acid in good yield and by means of simple processes.
The esters of polyalcohols, which have various uses for lubricating oils, plasticizers, toilet article bases, surface active agents and the like, have hitherto been manufactured by the reaction of natural fatty acids with polyalcohols. However, since natural fatty acids are unbalanced in carbon chain distribution and contain only a small amount of C.sub.6 -C.sub.10 fatty acids that are important as materials for aviation engine oils and thermally stable plasticizers, esterification of synthetic fatty acids has come to attract public attention from the view point of stable supply as the uses of the esters of polyalcohols are expanded.
As the methods of preparing synthetic fatty acids there are enumerated the Reppe process and the Koch process wherein olefins are used as starting materials, and in addition the Paraffin-Oxidation process wherein paraffin is used as starting material. In these processes, however, side-chain fatty acids are by-produced. As these side-chain fatty acids are extremely inferior in reactivity as compared with straight-chain fatty acids, it is difficult to synthesize the esters of polyalcohols directly from the synthetic fatty acids containing such side-chain fatty acids.
The so-called complex esters, which are obtained by esterifying the hydroxyl radicals remaining in the partial esters of polyalcohols available from polyalcohols and polycarboxylic acids with mono-carboxylic acids, are higher in viscosity and lower in pour point than esters obtained from natural fatty acids and polyalcohols, and therefore have wider uses for lubricating oil additives and so forth. The complex esters as aforesaid are normally obtained by esterifying polycarboxylic acid with polyalcohol and then reacting the residual hydroxyl radical with mono-carboxylic acid. According to this process, however, esterification must be conducted in two stages, the steps thereof becoming complicated.
In contrast, when polycarboxylic acid and mono-carboxylic acid are simultaneously esterified there occurs a problem that a large amount of partial ester of polycarboxylic acid is by-produced which deteriorates the quality of the complex ester.
Of course the hydroxyl radical being residual in this partial ester may be removed by esterifying it with monohydric alcohol. In this case, however, there must be used complicated steps as in the aforesaid two-stage process.
Accordingly, it is extremely difficult to manufacture the complex ester having the construction as aforesaid by means of such processes as are readily contemplated by those skilled in this art.